Batteries may be connected in series, parallel, or combination of both. Batteries connected in series have the positive terminal of one battery connected to the negative terminal of another battery. This configuration may increase the overall voltage but remain the same overall capacity. Batteries connected in parallel, on the other hand, have their like terminals connected together. In this configuration, the overall voltage remains the same but the overall capacity is increased.
When batteries are connected in parallel and configured to provide a high voltage, a current shock may be generated due to small internal resistance of batteries. If the value of the current shock is larger than required to meet the design criteria, it may cause severe side effect on batteries and other circuitry components. In worse situations, it may damage batteries and the entire circuitry.